Brake valves in brake systems of a vehicle, for example a commercial vehicle, comprise an electrical stage and a pneumatic stage in order to effect braking demanded by the driver by adjusting a corresponding brake pressure, in particular in operating brakes of a vehicle, in particular a commercial vehicle, and thereby to set an actual vehicle deceleration. To form the electrical stage, a sensor unit is disposed in the brake valve that determines an operating variable representing the driver's demand, for example an operating travel of a brake pedal, and depending thereon a brake pressure that is proportional to the brake pedal position is adjusted at the operating brakes by means of a suitable electronically actuated valve. In the event of a failure of the electrical stage, a fallback level can be formed by means of a mechanical actuation that also corresponds to the operating travel of the brake pedal.
One such brake valve with a braking value generator is described in EP 1000830 B1 and comprises an operating plunger that is deflected by the brake pedal against the force of two springs. The deflection is detected electrically by the sensor unit and analyzed. The electrical actuation of a brake pressure modulator then takes place, for example of a proportionality valve that adjusts a control pressure. With said control pressure an air quantity boosting relay valve is actuated, which ultimately produces the brake pressure corresponding to the driver's demand and may adjust the brake pressure while taking into account a load-dependent axle load distribution on the corresponding operating brakes. The conversion of the deflection, i.e. of the operating travel of the brake pedal, into the brake pressure or the control pressure for the relay valve is carried out by means of a previously determined feeling curve, which associates a brake/control pressure to be adjusted by the relay valve with the operating travel. The feeling curve is of a two-stage form in this case, whereby in a first stage a wear-free brake, for example a retarder, is actuated up to a minimum operating travel of the brake pedal and above the minimum operating travel an operating brake that is subject to wear is actuated with the corresponding brake pressure while possibly taking into account an axle load distribution.